Abstract:

Provided is a thermally-assisted magnetic recording head capable of
setting the near-field light (NFL-) emission point to be sufficiently
close to the write-field-generating portion. The head comprises a
magnetic pole, a waveguide propagating light, and a NFL-generator coupled
with the light in surface plasmon mode. The NFL-generator comprises a
propagation edge extending to the NFL-generating end surface, at least a
portion of the propagation edge being opposed to the waveguide with a
distance, and the magnetic pole has a surface contact with a surface
portion of the NFL-generator including no propagation edge. Therefore,
the distance between the magnetic-pole end surface and the NFL-generating
end surface becomes zero. The propagation edge is not contacted with the
magnetic pole. Accordingly, the surface plasmon can propagate along on
the propagation edge without being absorbed by the pole. Thus, the
NFL-emission point is ensured to be at the end point of the propagation
edge.

Claims:

1. A thermally-assisted magnetic recording head comprising:a magnetic pole
for generating write field from its end on an opposed-to-medium surface
side;a waveguide through which a light for exciting surface plasmon
propagates; anda near-field light generator provided between the magnetic
pole and the waveguide, configured to be coupled with the light in a
surface plasmon mode and to emit near-field light from a near-field light
generating end surface that forms a portion of the opposed-to-medium
surface,the near-field light generator comprising a propagation edge
extending to the near-field light generating end surface and being
configured to propagate thereon the surface plasmon excited by the light,
at least a portion of the propagation edge being opposed to the waveguide
with a predetermined distance, andthe magnetic pole having a surface
contact with a surface portion of the near-field light generator that
does not include the propagation edge.

2. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein the magnetic pole has a surface contact with all side surfaces of
the near-field light generator that do not have the propagation edge as
one of their boundaries.

3. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein the magnetic pole covers or one end surface of the magnetic pole
overlaps all side edges of the near-field light generator except the
propagation edge.

4. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein the near-field light generator comprises a groove extending to
the near-field light generating end surface on a side opposite to the
propagation edge, and a portion of the magnetic pole is embedded in the
groove.

5. The thermally-assisted magnetic recording head as claimed in claim 4,
wherein the groove is substantially V-shaped.

6. The thermally-assisted magnetic recording head as claimed in claim 4,
wherein a bottom of the groove is located at a distance along a track
from the propagation edge, and a distance on the opposed-to-medium
surface between the bottom of the groove and the propagation edge is 30
nanometers or more, and 100 nanometers or less.

7. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein a magnetic shield is provided on a side opposite to the magnetic
pole when viewed from the near-field light generator.

8. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein a buffering portion having a refractive index lower than that of
the waveguide is provided in a region including a sandwiched portion
between the waveguide and the propagation edge.

9. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein the near-field light generator is formed of a silver alloy
including at least one element selected from a group consisting of a
palladium, gold, copper, ruthenium, rhodium and iridium.

10. A head gimbal assembly comprising: a thermally-assisted magnetic
recording head as claimed in claim 1; and a suspension supporting the
thermally-assisted magnetic recording head.

11. A magnetic recording apparatus comprising:at least one head gimbal
assembly comprising: a thermally-assisted magnetic recording head; and a
suspension supporting the thermally-assisted magnetic recording head;at
least one magnetic recording medium; anda recording circuit configured to
control write operations that the thermally-assisted magnetic recording
head performs to the at least one magnetic recording medium,the
thermally-assisted magnetic recording head comprising:a magnetic pole for
generating write field from its end on an opposed-to-medium surface
side;a waveguide through which a light for exciting surface plasmon
propagates; anda near-field light generator provided between the magnetic
pole and the waveguide, configured to be coupled with the light in a
surface plasmon mode and to emit near-field light from a near-field light
generating end surface that forms a portion of the opposed-to-medium
surface,the near-field light generator comprising a propagation edge
extending to the near-field light generating end surface and being
configured to propagate thereon the surface plasmon excited by the light,
at least a portion of the propagation edge being opposed to the waveguide
with a predetermined distance,the magnetic pole having a surface contact
with a surface portion of the near-field light generator that does not
include the propagation edge, andthe recording circuit further comprising
a light-emission control circuit configured to control operations of a
light source that generates the light for exciting surface plasmon.

12. The magnetic recording apparatus as claimed in claim 11, wherein the
magnetic pole has a surface contact with all side surfaces of the
near-field light generator that do not have the propagation edge as one
of their boundaries.

13. The magnetic recording apparatus as claimed in claim 11, wherein the
magnetic pole covers or one end surface of the magnetic pole overlaps all
side edges of the near-field light generator except the propagation edge.

14. The magnetic recording apparatus as claimed in claim 11, wherein the
near-field light generator comprises a groove extending to the near-field
light generating end surface on a side opposite to the propagation edge,
and a portion of the magnetic pole is embedded in the groove.

15. The magnetic recording apparatus as claimed in claim 14, wherein the
groove is substantially V-shaped.

16. The magnetic recording apparatus as claimed in claim 14, wherein a
bottom of the groove is located at a distance along a track from the
propagation edge, and a distance on the opposed-to-medium surface between
the bottom of the groove and the propagation edge is 30 nanometers or
more, and 100 nanometers or less.

17. The magnetic recording apparatus as claimed in claim 11, wherein a
magnetic shield is provided on a side opposite to the magnetic pole when
viewed from the near-field light generator.

18. The magnetic recording apparatus as claimed in claim 11, wherein a
buffering portion having a refractive index lower than that of the
waveguide is provided in a region including a sandwiched portion between
the waveguide and the propagation edge.

19. The magnetic recording apparatus as claimed in claim 11, wherein the
near-field light generator is formed of a silver alloy including at least
one element selected from a group consisting of a palladium, gold,
copper, ruthenium, rhodium and iridium.

20. The thermally-assisted magnetic recording head as claimed in claim 1,
wherein an end surface of the waveguide on the opposed-to-medium surface
side lies behind the opposed-to-medium surface of the head when viewed
from outside of the head on the opposed-to-medium surface side.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a head used for thermally-assisted
magnetic recording in which a magnetic recording medium is irradiated
with near-field light (NF-light), thereby anisotropic magnetic field of
the medium is lowered, thus data can be written. The present invention
especially relates to a thermally-assisted magnetic recording head
provided with a near-field light generator (NFL-generator) that converts
light received from a waveguide into NF-light. Further, the present
invention relates to a magnetic recording apparatus provided with the
head.

[0003]2. Description of the Related Art

[0004]As the recording densities of magnetic recording apparatuses become
higher, as represented by magnetic disk apparatuses, further improvement
has been required in the performance of thin-film magnetic heads and
magnetic recording media. In the magnetic recording media, it is
especially necessary to decrease the size of magnetic grains that
constitute a magnetic recording layer of the medium and to reduce
irregularity in the boundary of record bit in order to improve the
recording density. However, the decrease in size of the magnetic grains
raises a problem of degradation in thermal stability of the magnetization
due to the decrease in volume. As a measure against the thermal stability
problem, it may be possible to increase magnetic anisotropy energy
KU of the magnetic grains. However, the increase in energy KU
causes the increase in anisotropic magnetic field (coercive force) of the
magnetic recording medium. As a result, the head cannot write data to the
magnetic recording medium when the anisotropic magnetic field (coercive
force) of the medium exceeds the write field limit.

[0005]Recently, as a method for solving the problem of thermal stability,
so-called a thermally-assisted magnetic recording technique is proposed.
In the technique, a magnetic recording medium formed of a magnetic
material with a large magnetic anisotropy energy KU is used so as to
stabilize the magnetization; anisotropic magnetic field of the medium is
reduced by applying heat to a portion of the medium where data is to be
written; just after that, writing is performed by applying write magnetic
field (write field) to the heated portion.

[0006]In the thermally-assisted magnetic recording, a technique is well
known, which utilizes a near-field light generator (NFL-generator) as a
metal piece that generates near-field light (NF-light) from plasmon
excited by irradiated laser light. For example, U.S. Pat. No. 6,768,556
and U.S. Pat. No. 6,649,894 disclose a technique in which NF-light is
generated by irradiating a metal scatterer with light and by matching the
frequency of the light with the resonant frequency of plasmon excited in
the metal.

[0007]As described above, various kinds of thermally-assisted magnetic
recording systems with NFL-generators have been proposed. Meanwhile, the
present inventors have devised a NFL-generator in which laser light is
coupled with the NFL-generator in a surface plasmon mode to cause excited
surface plasmon to propagate to the opposed-to-medium surface, thereby
providing NF-light, instead of directly applying the laser light to a
NFL-generator. The NFL-generator is hereinafter referred to as a surface
plasmon generator. In the surface plasmon generator, its temperature does
not excessively rise because laser light is not directly applied to the
surface plasmon generator. As a result, there can be avoided a situation
in which the end of a read head element, which reaches the
opposed-to-medium surface, becomes relatively far apart from the magnetic
recording medium due to the thermal expansion of the generator, which
makes it difficult to properly read servo signals during recording
operations. In addition, there can also be avoided a situation in which
the light use efficiency of a near-field light generating
(NFL-generating) optical system including the NFL-generator is degraded
because thermal fluctuation of free electrons increases in the
NFL-generator.

[0008]Here, the NFL-generating optical system is an optical system that
includes a waveguide and a NFL-generator, and the light use efficiency of
the NFL-generating optical system is given by
IOUT/IIN(×100), where IIN is the intensity of laser
light incident to the waveguide, and IOUT is the intensity of
NF-light emitted from a NFL-generating end of the generator after
converting the laser light into surface plasmon in the NFL-generator.

[0009]To perform thermal-assisted magnetic recording in practice by using
the above-described NFL-generating optical system including the surface
plasmon generator, the end surface of the surface plasmon generator is
required to be located as close to the end surface of magnetic pole as
possible in the opposed-to-medium surface, the magnetic pole generating
write field. In particular, the distance between them in the direction
along track is preferably set to 100 nm or less. Further, the distance
between the emitting position of NF-light on the end surface of the
surface plasmon generator and the generating position of write field on
the magnetic-pole end surface is required to be set sufficiently small.
By satisfying these conditions, there can be obtained a sufficiently
large field gradient of write field generated from the magnetic pole in a
position on the magnetic recording medium where NF-light is applied.

[0010]However, the NFL-generator is provided adjacent to the end portion
on the opposed-to-medium surface side of the waveguide to convert the
light propagating through the waveguide into NF-light. Here, the
waveguide and the magnetic pole is required to be provided sufficiently
apart from each other in order to avoid a situation in which the light
use efficiency of the NFL-generating optical system is drastically
reduced due to the absorption of the light propagating through the
waveguide by the magnetic pole formed of a metal. This requirement
conflicts with the requirement that the NFL-generator and the magnetic
pole should be set as close as possible. Therefore, to resolve the
conflict, important is the appropriate configuration and arrangement of
the waveguide, the NFL-generator and the magnetic pole. Further,
significantly important is the control of the emitting position of
NF-light on the end surface of the surface plasmon generator. Thus, it is
understood that there exists a significantly important problem that, in
order to perform appropriate thermally-assisted magnetic recording, a
NFL-generating optical system in which a NFL-generator with an adjusted
emitting position can be provided adjacent to the magnetic pole should be
realized.

SUMMARY OF THE INVENTION

[0011]Some terms used in the specification will be defined before
explaining the present invention. In a layered structure or an element
structure formed on an element-formation surface of a slider substrate of
the magnetic recording head according to the present invention, when
viewed from a standard layer or element, a substrate side is defined as
"lower" side, and the opposite side as an "upper" side. Further, "X-, Y-
and Z-axis directions" are indicated in some figures showing embodiments
of the head according to the present invention as needed. Here, Z-axis
direction indicates above-described "up-and-low" direction, and +Z
direction corresponds to a trailing side and -Z direction to a leading
side. And Y-axis direction indicates a track width direction, and X-axis
direction indicates a height direction.

[0012]Further, a "side surface" of a waveguide provided within the
magnetic recording head is defined as an end surface other than the end
surfaces perpendicular to the direction in which light propagates within
the waveguide (-X direction), out of all the end surfaces surrounding the
waveguide. According to the definition, an "upper surface" and a "lower
surface" are one of the "side surfaces". The "side surface" is a surface
on which the propagating light can be totally reflected within the
waveguide corresponding to a core. Further, a "side surface" of a
NFL-generator (surface plasmon generator) provided within the magnetic
recording head is defined as an end surface other than the NFL-generating
end surface of the NFL-generator and the end surface opposed to the
NFL-generating end surface. Actually, some of the "side surfaces" include
a propagation edge described later as a boundary of them.

[0013]According to the present invention, a thermally-assisted magnetic
recording head is provided, which comprises:

[0014]a magnetic pole for generating write field from its end on an
opposed-to-medium surface side;

[0015]a waveguide through which a light for exciting surface plasmon
propagates; and

[0016]a NFL-generator provided between the magnetic pole and the
waveguide, configured to be coupled with the light in a surface plasmon
mode and to emit near-field light (NF-light) from a NFL-generating end
surface that forms a portion of the opposed-to-medium surface,

[0017]the NFL-generator comprising a propagation edge extending to the
NFL-generating end surface and being configured to propagate thereon the
surface plasmon excited by the light, at least a portion of the
propagation edge being opposed to the waveguide with a predetermined
distance, and

[0018]the magnetic pole having a surface contact with a surface portion of
the NFL-generator that does not include the propagation edge.

[0019]In the thermally-assisted magnetic recording head according to the
present invention, since the magnetic pole is in surface contact with the
NFL-generator, the distance between the end surface of the magnetic pole
that generates write field and the NFL-generating end surface of the
NFL-generator is zero. On the other hand, the propagation edge of the
NFL-generator is not in contact with the magnetic pole at all.
Accordingly, the excited surface plasmon can propagate along on the
propagation edge without being absorbed by the magnetic pole. As a
result, the NF-light emission point on the NFL-generating end surface of
the NFL-generator is located at one of the vertices of the NFL-generating
end surface, and is a vertex that corresponds to the end of the
propagation edge that is not in contact with the magnetic pole. This can
ensure that the NF-light emission point is established in a location
sufficiently close to the end surface of the magnetic pole that generates
write field.

[0020]Further, by using the above-described thermally-assisted magnetic
recording head, a write field having a sufficiently large gradient can be
applied to a sufficiently heated portion in the magnetic recording layer
of a magnetic recording medium. Consequently, a thermally-assisted,
stable write operation can be ensured.

[0021]Further, in the above-described thermally-assisted magnetic
recording head according to the present invention, the magnetic pole
preferably has a surface contact with all side surfaces of the
NFL-generator that do not have the propagation edge as one of their
boundaries. And it is preferable that the magnetic pole covers or one end
surface of the magnetic pole overlaps all side edges of the NFL-generator
except the propagation edge. Further, the NFL-generator preferably
comprises a groove extending to the NFL-generating end surface on a side
opposite to the propagation edge, and a portion of the magnetic pole is
preferably embedded in the groove. In the case, it is preferable that the
groove is substantially V-shaped. This means that the magnetic pole has a
very small write-field generating point, thereby to contribute to the
achievement of higher recording density. Furthermore, the distance
between the write-field generating point and the NFL-generating emission
point can be set sufficiently small. In practice, in the case that the
bottom of the groove is located at a distance along the track from the
propagation edge, the distance on the opposed-to-medium surface between
the bottom of the groove and the propagation edge is preferably 30 nm
(nanometers) or more, and 100 nm or less.

[0022]Further, in the above-described thermally-assisted magnetic
recording head according to the present invention, a magnetic shield is
preferably provided on a side opposite to the magnetic pole when viewed
from the NFL-generator. And a buffering portion having a refractive index
lower than that of the waveguide is preferably provided in a region
including a sandwiched portion between the waveguide and the propagation
edge. Further, the NFL-generator is preferably formed of a silver alloy
including at least one element selected from a group consisting of a
palladium, gold, copper, ruthenium, rhodium and iridium.

[0023]According to the present invention, a head gimbal assembly (HGA) is
further provided, which comprises: the above-described thermally-assisted
magnetic recording head; and a suspension supporting the
thermally-assisted magnetic recording head. Furthermore, according to the
present invention, a magnetic recording apparatus is provided, which
comprises: the above-described HGA; at least one magnetic recording
medium; and a recording circuit configured to control write operations
that the thermally-assisted magnetic recording head performs to the at
least one magnetic recording medium, the recording circuit further
comprising a light-emission control circuit configured to control
operations of a light source that generates the light for exciting
surface plasmon.

[0024]Further objects and advantages of the present invention will be
apparent from the following description of preferred embodiments of the
invention as illustrated in the accompanying figures. In each figure, the
same element as an element shown in other figure is indicated by the same
reference numeral. Further, the ratio of dimensions within an element and
between elements becomes arbitrary for viewability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 shows a perspective view schematically illustrating a
structure of a major part in one embodiment of a magnetic recording
apparatus and an HGA according to the present invention;

[0026]FIG. 2 shows a perspective view illustrating one embodiment of
thermally-assisted magnetic recording head according to the present
invention;

[0027]FIG. 3 shows a cross-sectional view taken by plane A in FIG. 2,
schematically illustrating the structure of a main part of the
thermally-assisted magnetic recording head according to the present
invention;

[0028]FIG. 4 shows a perspective view schematically illustrating the
configuration of the waveguide, the surface plasmon generator and the
main magnetic pole;

[0029]FIG. 5 shows a plain view illustrating the shapes of the end
surfaces of the waveguide, the surface plasmon generator and the
electromagnetic transducer on the head part end surface or in its
vicinity;

[0030]FIG. 6 shows a schematic view for explaining the thermally-assisted
magnetic recording utilizing a surface plasmon mode according to the
present invention;

[0031]FIGS. 7a to 7d show schematic views illustrating various embodiments
regarding the NFL-generating optical system and the main magnetic pole
according to the present invention;

[0032]FIGS. 8a to 8f show schematic views illustrating an embodiment of
processes for forming the surface plasmon generator having the groove and
the main magnetic pole according to the present invention;

[0033]FIG. 9 shows a schematic view illustrating a system used in the
simulation analysis experiment;

[0035]FIGS. 11a and 11b show cross-sectional views taken by ZX-plane,
schematically illustrating thermally-assisted magnetic recording heads
used in the practical example and the comparative example, respectively;

[0036]FIG. 11c shows a cross-sectional view taken by XY-plane included in
an upper yoke layer, schematically illustrating the thermally-assisted
magnetic recording head used in the practical and comparative examples;
and

[0037]FIG. 12 shows a graph illustrating intensity distributions of
effective write fields in the practical example and the comparative
example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038]FIG. 1 shows a perspective view schematically illustrating a
structure of a major part in one embodiment of a magnetic recording
apparatus and an HGA according to the present invention. Here, in the
perspective view of the HGA, the side of the HGA, which is opposed to the
surface of the magnetic recording medium, is presented as the upper side.

[0039]A magnetic disk apparatus as a magnetic recording apparatus shown in
FIG. 1 includes: a plurality of magnetic disks 10 as magnetic recording
media, rotating around a rotational axis of a spindle motor 11; an
assembly carriage device 12 provided with a plurality of drive arms 14
therein; a head gimbal assembly (HGA) 17 attached on the top end portion
of each drive arm 14 and provided with a thermally-assisted magnetic
recording head 21 as a thin-film magnetic head; and a
recording/reproducing and light-emission control circuit 13 for
controlling write/read operations of the thermally-assisted magnetic
recording head 21 and further for controlling the emission operation of a
laser diode as a light source that generates laser light used for
thermally-assisted magnetic recording, which will be described later.

[0040]In the present embodiment, the magnetic disk 10 is designed for
perpendicular magnetic recording, and has a structure in which
sequentially stacked on a disk substrate is a soft-magnetic under layer,
an intermediate layer, and a magnetic recording layer (perpendicular
magnetization layer). The assembly carriage device 12 is a device for
positioning the thermally-assisted magnetic recording head 21 above a
track on which recording bits are aligned, the track being formed on the
magnetic recording layer of the magnetic disk 10. In the apparatus, the
drive arms 14 are stacked in a direction along a pivot bearing axis 16
and can be angularly swung around the axis 16 by a voice coil motor (VCM)
15. The structure of the magnetic disk apparatus according to the present
invention is not limited to that described above. For instance, the
number of each of magnetic disks 10, drive arms 14, HGAs 17 and
thermally-assisted magnetic recording heads 21 may be single.

[0041]Referring also to FIG. 1, a suspension 20 in the HGA 17 includes a
load beam 200, a flexure 201 with elasticity fixed to the load beam 200,
and a base plate 202 provided on the base portion of the load beam 200.
Further, on the flexure 201, there is provided a wiring member 203 that
is made up of lead conductors and connection pads electrically joined to
both ends of the lead conductors. The thermally-assisted magnetic
recording head 21 is fixed to the flexure 201 at the top end portion of
the suspension 20 so as to face the surface of the magnetic disk 10 with
a predetermined spacing (flying height). Moreover, one end of the wiring
member 203 is electrically connected to terminal electrodes of the
thermally-assisted magnetic recording head 21. The structure of the
suspension 20 is not limited to the above-described one. An IC chip for
driving the head may be mounted midway on the suspension 20, though not
shown.

[0042]FIG. 2 shows a perspective view illustrating one embodiment of
thermally-assisted magnetic recording head 21 according to the present
invention.

[0043]As shown in FIG. 2, a thermally-assisted magnetic recording head 21
is constituted of the slider 22 and the light source unit 23. The slider
22 includes: a slider substrate 220 formed of, for example, AlTiC
(Al2O3--TiC), and having an air bearing surface (ABS) 2200
processed so as to provide an appropriate flying height; and a head part
221 formed on an element-formation surface 2202 perpendicular to the ABS
2200. While, the light source unit 23 includes: a unit substrate 230
formed of, for example, AlTiC (Al2O3--TiC), and having an
joining surface 2300; and a laser diode 40 as a light source provided on
a source-installation surface 2302 perpendicular to the joining surface
2300. The slider 22 and the light source unit 23 are bonded to each other
in such a way that the back surface 2201 of the slider substrate 220 and
the joining surface 2300 of the unit substrate 230 have a surface contact
with each other. Here, the back surface 2201 of the slider substrate 220
is defined as an end surface opposite to the ABS 2200 of the slider
substrate 220. Alternatively, the thermally-assisted magnetic recording
head 21 may have a configuration in which the laser diode 40 is provided
directly on the slider 22 without using the light source unit 23.

[0044]In the slider 22, the head part 221 formed on the element-formation
surface 2202 of the slider substrate 220 includes: a head element 32
constituted of a magnetoresistive (MR) element 33 for reading data from
the magnetic disk and an electromagnetic transducer 34 for writing data
to the magnetic disk; a waveguide 35 for guiding laser light generated
from a laser diode 40 provided in the light source unit 23 to the
opposed-to-medium surface side; a surface plasmon generator 36, the
generator 36 and the waveguide 35 constituting a near-field-light
generating (NFL-generating) optical system; an overcoat layer 38 formed
on the element-formation surface 2202 in such a way as to cover the MR
element 33, the electromagnetic transducer 34, the waveguide 35, and the
surface plasmon generator 36; a pair of terminal electrodes 370 exposed
in the upper surface of the overcoat layer 38 and electrically connected
to the MR element 33; and a pair of terminal electrodes 371 also exposed
in the upper surface of the overcoat layer 38 and electrically connected
to the electromagnetic transducer 34. The terminal electrodes 370 and 371
are electrically connected to the connection pads of the wiring member
203 provided on the flexure 201 (FIG. 1).

[0045]One ends of the MR element 33, the electromagnetic transducer 34 and
the surface plasmon generator 36 reach a head part end surface 2210,
which is an opposed-to-medium surface of the head part 221. Here, the
head part end surface 2210 and the ABS 2200 constitute the whole
opposed-to-medium surface of the thermally-assisted magnetic recording
head 21. During actual write and read operations, the thermally-assisted
magnetic recording head 21 aerodynamically flies above the surface of the
rotating magnetic disk with a predetermined flying height. Thus, the ends
of the MR element 33 and electromagnetic transducer 34 face the surface
of the magnetic recording layer of the magnetic disk with an appropriate
magnetic spacing. Then, the MR element 33 reads data by sensing signal
magnetic field from the magnetic recording layer, and the electromagnetic
transducer 34 writes data by applying signal magnetic field to the
magnetic recording layer. When writing data, laser light generated from
the laser diode 40 of the light source unit 23 propagates through the
waveguide 35. Then, the propagating laser light is coupled with the
surface plasmon generator 36 in a surface plasmon mode, and causes
surface plasmon to be excited on the surface plasmon generator 36. The
surface plasmon propagates on a propagation edge provided in the surface
plasmon generator 36, which will be explained later, toward the head part
end surface 2210, which causes near-field light (NF-light) to be
generated from the end of the surface plasmon generator 36 on the head
part end surface 2210 side. The generated NF-light reaches the surface of
the magnetic disk, and heats a portion of the magnetic recording layer of
the magnetic disk. As a result, the anisotropic magnetic field (coercive
force) of the portion is decreased to a value that enables writing; thus
the thermally-assisted magnetic recording can be accomplished by applying
write field to the portion with decreased anisotropic magnetic field.

[0046]FIG. 3 shows a cross-sectional view taken by plane A in FIG. 2,
schematically illustrating the structure of a main part of the
thermally-assisted magnetic recording head 21.

[0047]As shown in FIG. 3, the MR element 33 is formed on an insulating
layer 380 stacked on the element-formation surface 2202, and includes: an
MR multilayer 332; and a lower shield layer 330 and an upper shield layer
334 which sandwich the MR multilayer 332 and an insulating layer 381
therebetween. The upper and lower shield layers 334 and 330 prevent the
MR multilayer 332 from receiving external magnetic field as a noise. The
MR multilayer 332 is a magneto-sensitive part for detecting signal
magnetic field by using MR effect. The MR multilayer 332 may be, for
example: a current-in-plane giant magnetoresistive (CIP-GMR) multilayer
that utilizes CIP-GMR effect; a current-perpendicular-to-plane giant
magnetoresistive (CPP-GMR) multilayer that utilizes CPP-GMR effect; or a
tunnel magnetoresistive (TMR) multilayer that utilizes TMR effect. The MR
multilayer 332 that utilizes any MR effect described above can detect
signal magnetic field from the magnetic disk with high sensitivity. In
the case that the MR multilayer 332 is a CPP-GMR multilayer or a TMR
multilayer, the upper and lower shield layers 334 and 330 act as
electrodes.

[0048]Referring also to FIG. 3, the electromagnetic transducer 34 is
designed for perpendicular magnetic recording, and includes an upper yoke
layer 340, a main magnetic pole 3400, a write coil layer 343, a
coil-insulating layer 344, a lower yoke layer 345, and a lower shield
3450.

[0049]The upper yoke layer 340 is formed so as to cover the
coil-insulating layer 344, and the main magnetic pole 3400 is formed on
an insulating layer 385 made of an insulating material such as
Al2O3 (alumina). These upper yoke layer 340 and main magnetic
pole 3400 are magnetically connected with each other, and acts as a
magnetic path for converging and guiding magnetic flux toward the
magnetic recording layer (perpendicular magnetization layer) of the
magnetic disk, the magnetic flux being excited by write current flowing
through the write coil layer 343. The main magnetic pole 3400 reaches the
head part end surface 2210, and the end surface 3400e of the pole 3400,
which is a portion of the end surface 2210, has a vertex closest to the
lower shield 3450 (most on the leading side), the vertex being a point
(WFP: FIG. 5) where write field is generated. This minute
write-field-generating point of the main magnetic pole 3400 enables a
fine write field responding to higher recording density to be generated.
The main magnetic pole 3400 is formed of a soft-magnetic material with a
saturation magnetic flux density higher than that of the upper yoke layer
340, which is, for example, an iron alloy containing Fe as a main
component, such as FeNi, FeCo, FeCoNi, FeN or FeZrN. The thickness of the
main magnetic pole is, for example, in the range of approximately 0.1 to
0.8 μm.

[0050]The write coil layer 343 is formed on an insulating layer 3421 made
of an insulating material such as Al2O3 (alumina), in such a
way as to pass through in one turn at least between the lower yoke layer
345 and the upper yoke layer 340, and has a spiral structure with a back
contact portion 3402 as a center. The write coil layer 343 is formed of a
conductive material such as Cu (copper). The write coil layer 343 is
covered with a coil-insulating layer 344 that is formed of an insulating
material such as a heat-cured photoresist and electrically isolates the
write coil layer 343 from the upper yoke layer 340. The write coil layer
343 has a monolayer structure in the present embodiment. However, the
write coil layer 343 may have a two or more layered structure, or may
have a helical coil shape in which the upper yoke layer 340 is sandwiched
therebetween as shown in FIGS. 11a and 11c. Further, the number of turns
of the write coil layer 343 is not limited to that shown in FIG. 3, and
may be, for example, in the range from two to seven.

[0051]The back contact portion 3402 has a though-hole extending in X-axis
direction, and the waveguide 35 and insulating layers that cover the
waveguide 35 pass through the though-hole. In the though-hole, the
waveguide 35 is away at a predetermined distance of, for example, at
least 1 μm from the inner wall of the back contact portion 3402. The
distance prevents the absorption of the waveguide light by the back
contact portion 3402.

[0052]The lower yoke layer 345 is formed on an insulating layer 383 made
of an insulating material such as Al2O3 (alumina), and acts as
a magnetic path for the magnetic flux returning from a soft-magnetic
under layer that is provided under the magnetic recording layer
(perpendicular magnetization layer) of the magnetic disk 10. The lower
yoke layer 345 is formed of a soft-magnetic material, and its thickness
is, for example, approximately 0.5 to 5 μm. Further, the lower shield
3450 is a magnetic shield that reaches the head part end surface 2210,
being magnetically connected with the lower yoke layer 345. The lower
shield 3450 is provided on the opposite side to the main magnetic pole
3400 from the surface plasmon generator 36, and acts for receiving the
magnetic flux spreading from the main magnetic pole 3400. The lower
shield 3450 has a width in the track width direction greatly larger than
that of the main magnetic pole 3400. This lower shield 3450 causes the
magnetic field gradient between the end portion of the lower shield 3450
and the main magnetic pole 3400 to become steeper. As a result, jitter of
signal output becomes smaller, and therefore, error rates during read
operations can be reduced. The lower shield 3450 is preferably formed of
a material with high saturation magnetic flux density such as NiFe
(Permalloy) or an iron alloy as the main magnetic pole 3400 is formed of.

[0053]Referring also to FIG. 3, the waveguide 35 and the surface plasmon
generator 36 are provided between the lower yoke layer 345 (lower shield
3450) and an upper yoke layer 340 (main magnetic pole 3400), and form an
optical system for generating NF-light in the head part 221. The
waveguide 35 is provided in parallel with an element-formation surface
2202 and extends from the rear end surface 352 which is a portion of the
head part rear end surface 2212 to the end surface 350 on the head part
end surface 2210 side. A portion of the upper surface (side surface) of
the waveguide 35 and a portion of the lower surface (including a
propagation edge 360) of the surface plasmon generator 36 are opposed to
each other with a predetermined distance therebetween. The portion
sandwiched between these portions forms a buffering portion 50 that has a
refractive index lower than that of the waveguide 35. The buffering
portion 50 couples laser light propagating through the waveguide 35 to
the surface plasmon generator 36 in a surface plasmon mode. The buffering
portion 50 may be a portion of the insulating layer 384 that is a part of
the overcoat layer 38 or may be a different layer provided in addition to
the insulating layer 384.

[0054]The surface plasmon generator 36 is located between the waveguide 35
and the main magnetic pole 3400, and includes a NFL-generating end
surface 36a that is a portion of the head part end surface 2210. The
surface plasmon generator 36 further includes a propagation edge 360 at
least a portion of which is opposed to the waveguide 35 across the
buffering portion 50 and extends to the NFL-generating end surface 36a.
The propagation edge 360 propagates surface plasmon excited by laser
light (waveguide light) that has propagated through the waveguide 35. The
surface plasmon generator 36 couples with the waveguide light in a
surface plasmon mode and propagates surface plasmon along on the
propagation edge 360 to emit NF-light from the NFL-generating end surface
36a.

[0055]The main magnetic pole 3400 is in surface contact with a surface
portion of the surface plasmon generator 36, the surface portion
excluding the propagation edge 360. In other words, the main magnetic
pole 3400 is in surface contact with all side surfaces of the surface
plasmon generator 36 that do not have the propagation edge 360 as one of
their boundaries. That is, the main magnetic pole 3400 covers or one end
surface of the main magnetic pole 3400 overlaps all side edges (extending
in X-axis direction) of the surface plasmon generator 36 except the
propagation edge 360. Since the main magnetic pole 3400 is in surface
contact with the surface plasmon generator 36, the distance between the
end surface 3400e of the main magnetic pole 3400 that generates write
field and the NFL-generating end surface 36a of the surface plasmon
generator 36 is zero. On the other hand, the propagation edge 360 of the
surface plasmon generator 36 is not in contact with the main magnetic
pole 3400 at all. Accordingly, the excited surface plasmon can propagate
along on the propagation edge 360 without being absorbed by the main
magnetic pole 3400. As a result, the NF-light emission point on the
NFL-generating end surface 36a of the surface plasmon generator 36 is
located at one of the vertices of the NFL-generating end surface 36a, and
is a vertex (vertex NFP: FIG. 5) that corresponds to the end of the
propagation edge 360 that is not in contact with the main magnetic pole
3400. This can ensure that the NF-light emission point is established in
a location sufficiently close to the end surface 3400e of the main
magnetic pole 3400 that generates write field.

[0056]A detailed explanation of the waveguide 35, the buffering portion
50, the surface plasmon generator 36 and the main magnetic pole 3400 will
be given later with reference to FIG. 4. Further, as is in the present
embodiment, an inter-element shield layer 39 is preferably provided
between the MR element 33 and the electromagnetic transducer 34,
sandwiched by the insulating layers 382 and 383. The inter-element shield
layer 39 may be formed of a soft-magnetic material, and plays a role for
shielding the MR element 33 from magnetic field generated from the
electromagnetic transducer 34.

[0057]Also according to FIG. 3, the light source unit 23 includes: a unit
substrate 230; a laser diode 40 provided on the source-installation
surface 2302 of the unit substrate 230; a terminal electrode 410
electrically connected to the lower surface 401 as an electrode of the
laser diode 40; and a terminal electrode 411 electrically connected to
the upper surface 403 as an electrode of the laser diode 40. The terminal
electrodes 410 and 411 are electrically connected to the connection pads
of the wiring member 203 provided on the flexure 201 (FIG. 1). By
applying a predetermined voltage between both electrodes 410 and 411 of
the laser diode 40, laser light is emitted from the emission center on an
emission surface 400 of the laser diode 40. Here, in the configuration of
the head as shown in FIG. 3, the oscillation of electric field component
of the laser light generated from the laser diode 40 preferably has a
direction perpendicular to the stacking surface of the active layer 40e
(Z-axis direction). That is, the laser diode 40 preferably generates a
laser light with TM polarization. This enables the laser light
propagating through the waveguide 35 to be coupled with the surface
plasmon generator 36 through the buffering portion 50 in a surface
plasmon mode.

[0058]A light source such as InP base, GaAs base or GaN base diode can be
utilized as the laser diode 40, which is usually used for communication,
optical disk storage or material analysis. The wavelength λL,
of the radiated laser light may be, for example, in the range of
approximately 375 nm (nanometers) to 1.7 μm. Specifically, for
example, a laser diode of InGaAsP/InP quaternary mixed crystal can also
be used, in which possible wavelength region is set to be from 1.2 to
1.67 μm. The laser diode 40 has a multilayered structure including an
upper-electrode 40a, an active layer 40e, and a lower-electrode 40i. On
the front and rear cleaved surfaces of the multilayered structure of the
laser diode 40, respectively formed are reflective layers for exciting
the oscillation by total reflection. Further, the reflective layer 42 has
an opening in the position of the active layer 40e including the
light-emission center 4000. Here, the laser diode 40 has a thickness
TLA in the range of, for example, approximately 60 to 200 μm.

[0059]Further, an electric source provided within the magnetic disk
apparatus can be used for driving the laser diode 40. In fact, the
magnetic disk apparatus usually has an electric source with applying
voltage of, for example, approximately 2V, which is sufficient for the
laser oscillation. The amount of electric power consumption of the laser
diode 40 is, for example, in the order of several tens mW, which can be
covered sufficiently by the electric source provided within the magnetic
disk apparatus. The laser diode 40 and terminal electrodes 410 and 411
are not limited to the above-described embodiment. For example, the
electrodes of the laser diode 40 can be turned upside down, thus the
n-electrode 40a may be bonded to the source-installation surface 2302 of
the unit substrate 230. Further, alternatively, a laser diode may be
provided on the element-formation surface 2202 of the thermally-assisted
magnetic recording head 21, and then can be optically connected with the
waveguide 35. Furthermore, the thermally-assisted magnetic recording head
21 may include no laser diode 40; then, the light-emission center of a
laser diode provided within the magnetic disk apparatus and the rear-end
surface 352 of the waveguide 35 may be connected by using, for example,
optical fiber.

[0060]Each of the slider 22 and light source unit 23 may have an arbitrary
size. For example, the slider 22 may be so-called a femto slider in which
the width in the track width direction (Y-axis direction) is 700 μm;
the length (in Z-axis direction) is 850 μm; and the thickness (in
X-axis direction) is 230 μm. In the case, the light source unit 23 may
be one size smaller than the slider 22, and may have a size, for example,
in which the width in the track width direction is 425 μm; the length
is 300 μm; and the thickness is 300 μm.

[0061]By joining the above-described light source unit 23 and slider 22,
constituted is the thermally-assisted magnetic recording head 21. In the
joining, the joining surface 2300 of the unit substrate 230 is made
having a surface contact with the back surface 2201 of the slider
substrate 220. Then, the locations of the unit substrate 230 and the
slider substrate 220 are determined in such a way that the laser light
generated from the laser diode 40 can directly enter the waveguide 35
through the rear-end surface 352 opposite to the ABS 2200 of the
waveguide 35.

[0062]FIG. 4 shows a perspective view schematically illustrating the
configuration of the waveguide 35, the surface plasmon generator 36 and
the main magnetic pole 3400. In the figure, the head part end surface
2210 is positioned at the left side, the end surface 2210 including
positions where write field and NF-light are emitted toward the magnetic
recording medium.

[0063]Referring to FIG. 4, there are provided a waveguide 35 that
propagates laser light 53 for generating NF-light and a surface plasmon
generator 36 including an propagation edge 360 on which surface plasmon
excited by the laser light (waveguide light) 53 propagates. The surface
plasmon generator 36 further includes a NFL-generating end surface 36a
that reaches the head part end surface 2210. A portion between a portion
of the side surface 354 of the waveguide 35 and a portion of lower
surfaces (side surfaces) 36s1 and 36s2 including the
propagation edge 360 of the surface plasmon generator 36 forms a
buffering portion 50. That is, the propagation edge 360 is covered with
the buffering portion 50. The buffering portion 50 couples waveguide
light 53 to the surface plasmon generator 36 in a surface plasmon mode.
The propagation edge 360 propagates surface plasmon excited by the
waveguide light 53 to the NFL-generating end surface 36a.

[0064]The term "side surfaces" of the surface plasmon generator 36 as used
herein refers to end surfaces 36s1, 36s2, 36s3, 36s4,
36s5, and 36s6 except the NFL-generating end surface 36a and
the end surface opposed to the NFL-generating end surface 36a in X-axis
direction. Further, the term "side surfaces" of the waveguide 35 as used
herein refers to the end surfaces 351, 353, and 354 among the surrounding
end surfaces of the waveguide 35 except the end surface 350 on the head
part end surface 2210 side and the rear end surface 352 opposite to the
end surface 350. The side surfaces of the waveguide 35 are capable of
totally reflecting waveguide light 53 propagating through the waveguide
35 that acts as a core. In the present embodiment, the side surface 354
of the waveguide 35 a portion of which is in surface contact with the
buffering portion 50 is the upper surface of the waveguide 35. The
buffering portion 50 may be a portion of the overcoat layer 38 (FIG. 2),
or may be a different layer provided in addition to the overcoat layer
38.

[0065]More specifically, waveguide light 53 that has traveled to a close
proximity to the buffering portion 50 is coupled with the optical
configuration including the waveguide 35 having a refractive index of
nWG, the buffering portion 50 having a refractive index of nBF
and the surface plasmon generator 36 made of a conductive material such
as a metal, to induce a surface plasmon mode in the propagation edge 360
of the surface plasmon generator 36. That is, the waveguide light 53
couples to the surface plasmon generator 36 in the surface plasmon mode.
The induction of the surface plasmon mode is enabled by setting the
refractive index nBF of the buffering portion 50 to be smaller than
the refractive index nWG of the waveguide 35 (nBF<nWG).
In practice, evanescent light is excited in the buffering portion 50
under optical conditions at the interface between the waveguide 35 as a
core and the buffering portion 50. Then, the evanescent light is combined
with charge fluctuations caused on the surface (the propagation edge 360)
of the surface plasmon generator 36 to induce the surface plasmon mode
and excite surface plasmon 60. The propagation edge 360 is provided at
the location closest to the waveguide 35 on the inclined lower surfaces
(side surfaces) 36s1 and 36s2 of the surface plasmon generator
36, and is a corner edge where electric fields tend to concentrate;
thereby surface plasmon 60 is highly likely to be excited.

[0066]In the embodiment shown in FIG. 4, the surface plasmon generator 36
substantially has a shape of triangular prism extending in X-axis
direction in which a substantially V-shaped groove 51 that extends to the
NFL-generating end surface 36a is provided in the upper surface on the
side opposite to the propagation edge 360. The walls of the groove 51 are
side surfaces 36s4 and 36s5, and the bottom of the groove 51
forms an side edge 363. A portion 3400a of the main magnetic pole 3400 is
embedded in the groove 51. The groove 51 is filled with the portion
3400a.

[0067]Since the portion 3400a of the main magnetic pole 3400 is embedded
in the groove 51, the main magnetic pole 3400 is in surface contact with
all side surfaces 36s3, 36s4, 36s5 and 36s6 of the
surface plasmon generator 36 that do not have the propagation edge 360 as
one of their boundaries. Each of the side surfaces 36s1 and
36s2 of the surface plasmon generator 36 has the propagation edge
360 as one of their boundaries. In other words, the main magnetic pole
3400 covers or one end surface of the main magnetic pole 3400 overlaps
all edges 361, 362, 363, 364 and 365 (extending in X-axis direction) of
the surface plasmon generator 36 except the propagation edge 360. In the
present embodiment, the main magnetic pole 3400 is in contact with the
edges 361 and 365 and covers the edges 362, 363 and 364.

[0068]In this way, the main magnetic pole 3400 is in surface contact with
the surface plasmon generator 36, and therefore the distance between the
end surface 3400e of the main magnetic pole 3400 that generates write
field and the NFL-generating end surface 36a of the surface plasmon
generator 36 is zero. On the other hand, only the propagation edge 360 of
the surface plasmon generator 36 among the edges of the generator 36 is
positioned at a distance from the main magnetic pole 3400. Accordingly,
excited surface plasmon can propagate along on the propagation edge 360
without being absorbed by the main magnetic pole 3400. As a result, the
NF-light emission point on the NFL-generating end surface 36a of the
surface plasmon generator 36 is one of the vertices of the NFL-generating
end surface 36a, and is a vertex (vertex NFP: FIG. 5) that is the end of
the propagation edge 360 that is not contact with the main magnetic pole
3400 at all. Since only the propagation edge 360 is not covered or in
contact with the main magnetic pole 3400, surface plasmon can be
intentionally propagated along on the propagation edge 360 and the
NF-light emission point can be reliably set at the vertex NFP (FIG. 5)
that is sufficiently close to the end surface 3400e of the main magnetic
pole 3400 that generates write field. The propagation edge 360 is rounded
in order to prevent surface plasmon from running off the propagation edge
360 and to avoid reduction of the light use efficiency. The radius of
curvature of the rounded edge is preferably in the range from 6.25 to 20
nm.

[0069]The surface plasmon generator 36 is preferably made of silver (Ag)
or an Ag alloy mainly containing Ag. The alloy preferably contains at
least one element selected from the group consisting of a palladium (Pd),
gold (Au), copper (Cu), ruthenium (Ru), rhodium (Rh), and iridium (Ir).
By forming the surface plasmon generator 36 from such an Ag alloy, the
NF-light emission efficiency second to Ag, which is a material having
theoretically the highest NF-light emission efficiency, can be achieved
and, in addition, defects such as cracking and chipping of the
propagation edge 360 can be sufficiently minimized.

[0070]Referring again to FIG. 4, the waveguide 35 is provided on the -z
side (leading side) of the surface plasmon generator 36, that is, on the
side opposite to the main magnetic pole 3400 when viewed from the
waveguide 35. In this configuration, the waveguide 35 can be located at a
distance from the main magnetic pole 3400 even though the end surface
3400e of the main magnetic pole 3400 that generates write field is in
contact with the NFL-generating end surface 36a that generates NF-light.
This can prevent reduction in the amount of the waveguide light 53 to be
converted into NF-light due to partial absorption of the waveguide light
53 into the main magnetic pole 3400 made of a metal.

[0071]The waveguide 35 may have a shape with a constant width in the track
width direction (Y-axis direction), or as shown in FIG. 4, may have a
portion on the head part end surface 2210 side, which has a narrower
width in the track width direction (Y-axis direction). The width
WWG1 in the track width direction (Y-axis direction) of a portion of
the waveguide 35 on the rear end surface 352 side may be, for example, in
the range approximately from 0.5 to 200 μm, the rear end surface 352
being opposite to the head part end surface 2210 in the waveguide 35. The
width WWG2 in the track width direction (Y-axis direction) of a
portion of the waveguide 35 on the end surface 350 side may be, for
example, in the range approximately from 0.3 to 100 μm. And the
thickness TWG (in Z-axis direction) of a portion on the rear end
surface 352 side may be, for example, in the range approximately from 0.1
to 4 μm, and the height (length) HWG (in X-axis direction) may
be, for example, in the range approximately from 10 to 300 μm.

[0072]Further, the side surfaces of the waveguide 35: the upper surface
354; the lower surface 353; and both the side surfaces 351 in the track
width direction (Y-axis direction) have a surface contact with the
overcoat layer 38 (FIG. 2), that is, the insulating layers 384 and 385
(FIG. 3), except the portion having a surface contact with the buffering
portion 50. Here, the waveguide 35 is formed of a material with a
refractive index nWG higher than a refractive index nOC of the
constituent material of the overcoat layer 38, made by using, for
example, a sputtering method. For example, in the case that the
wavelength λL of laser light is 600 nm and the overcoat layer
38 is formed of SiO2 (silicon dioxide: n=1.5), the waveguide 35 can
be formed of, for example, Al2O3 (alumina: n=1.63). Further, in
the case that the overcoat layer 38 is formed of Al2O3
(n=1.63), the waveguide 35 can be formed of, for example,
SiOXNY (n=1.7-1.85), Ta2O5 (n=2.16), Nb2O5
(n=2.33), TiO (n=2.3-2.55) or TiO2 (n=2.3-2.55). This material
structure of the waveguide 35 enables the propagation loss of laser light
53 to be reduced due to the excellent optical characteristics of the
constituent material. Further, the existence of the waveguide 35 as a
core and the overcoat layer 38 as a clad can provide total reflection
conditions in all the side surfaces. As a result, more amount of laser
light 53 can reach the position of the buffering portion 50, which
improves the propagation efficiency of the waveguide 35. Meanwhile, in
the present embodiment, a portion of propagation edge 360 that is not
opposed to the waveguide 35 (buffering portion 50) may be covered with
the constituent material of the overcoat layer 38 having refractive index
nOC, for example, with a portion 3850 of the insulating layer 385.

[0073]Further, alternatively, the waveguide 35 may have a multilayered
structure of dielectric materials in which the upper a layer is in the
multilayered structure, the higher becomes the refractive index n of the
layer. The multilayered structure can be realized, for example, by
sequentially stacking dielectric materials of SiOXNY with the
composition ratios X and Y appropriately changed. The number of stacked
layers may be, for example, in the range from 8 to 12. In the case that
laser light 53 has a linear polarization in Z-axis direction, the
above-described structure enables the laser light 53 to propagate in the
position closer to the buffering portion 50. In this case, by choosing
the composition and layer thickness in each layer, and the number of
layers of the multilayered structure, the laser light 53 can propagate in
the desired position in Z-axis direction.

[0074]The surface plasmon generator 36 can have a width WNF in the
track width direction (Y-axis direction) in the upper surface 361, the
width WNF being sufficiently smaller than the wavelength of laser
light 53, for example, of approximately 10 to 100 nm. And the surface
plasmon generator 36 can have a thickness TNF (in Z-axis direction)
sufficiently smaller than the wavelength of the laser light 53, for
example, of approximately 10 to 100 nm. Further, the length (height)
HNF (in X-axis direction) can be set to be, for example, in the
range of, approximately 0.8 to 6.0 μm.

[0075]The buffering portion 50 is formed of a dielectric material having a
refractive index nBF lower than the refractive index nWG of the
waveguide 35. For example, when the wavelength λL of laser
light is 600 nm and the waveguide 35 is formed of Al2O3
(alumina: n=1.63), the buffering portion 50 may be formed of SiO2
(silicon dioxide: n=1.46). Further, when the waveguide 35 is formed of
Ta2O5 (n=2.16), the buffering portion 50 may be formed of
SiO2 (n=1.46) or Al2O3 (n=1.63). In these cases, the
buffering portion 50 can be a portion of the overcoat layer 38 (FIG. 2)
serving as a clad made of SiO2 (n=1.46) or Al2O3 (n=1.63).
Further, the length LBF (in X-axis direction) of a portion of the
buffering portion 50, the portion being sandwiched between the side
surface 354 of the waveguide 35 and the propagation edge 360, is
preferably in the range of 0.5 to 5 μm, and is preferably larger than
the wavelength λL of the laser light 53. In this preferable
case, the coupled portion has an area markedly larger than a so-called
"focal region" in the case that, for example, laser light is converged on
a buffering portion 50 and a surface plasmon generator 36 and is coupled
in a surface plasmon mode. As a result, very stable coupling in the
surface plasmon mode can be achieved. The thickness TBF of the
buffering portion 50 is preferably set to be, for example, in the range
of 10 to 200 nm. The length LBF and the thickness TBF of the
buffering portion 50 are important parameters for obtaining proper
excitation and propagation of surface plasmon.

[0076]As also shown in FIG. 4, the surface plasmon generator 36 is in
surface contact with the main magnetic pole 3400. Accordingly, heat
generated from the surface plasmon generator 36 when generating NF-light
can be partially dissipated into the main magnetic pole 3400. That is,
the main magnetic pole 3400 can be used as a heatsink. As a result,
excessive rise of temperature of the surface plasmon generator 36 can be
suppressed, and an unnecessary protrusion of the NFL-generating end
surface 36a and a substantial reduction in light use efficiency in the
surface plasmon generator 36 can be avoided. Furthermore, since the
surface plasmon generator 36 made of a metal is in contact with the main
magnetic pole 3400 also made of a metal, the surface plasmon generator 36
is not electrically isolated and therefore detrimental effects of
electrostatic discharge (ESD) can be inhibited.

[0077]FIG. 5 shows a plain view illustrating the shapes of the end
surfaces of the waveguide 35, the surface plasmon generator 36 and the
electromagnetic transducer 34 on the head part end surface 2210 or in its
vicinity.

[0078]As shown in FIG. 5, in the electromagnetic transducer 34, the main
magnetic pole 3400 and the lower shield 3450 reach the head part end
surface 2210. The end surface 3400e of the main magnetic pole 3400 on the
head part end surface 2210 has a combined shape of a trailing-side
portion having, for example, a substantially rectangular, square, or
trapezoidal shape and a leading-side portion 3400ae having, for example,
a substantially triangular shape embedded in the groove 51 of the surface
plasmon generator 36. The vertex WFP most on the leading side in the end
surface 3400e is closest to the lower shield 3450, and therefore magnetic
fields are most concentrated at the vertex WFP; thus the vertex WFP
becomes a write-field generating point. Since the main magnetic pole 3400
has such a small write-field generating point, a minute write field that
meets higher recording density can be generated.

[0079]The NFL-generating end surface 36a of the surface plasmon generator
36 on the head part end surface 2210 has a shape similar to a V-shape
with a predetermined thickness, and is in contact with the end surface
3400e of the main magnetic pole 3400 on the leading side (-Z side) of the
surface 3400e. One side edge of the end surface 3400e overlaps with all
the side edges that do not end at the vertex NFP, which is the end of the
propagation edge 360, among the six side edges of the NFL-generating end
surface 36a. In other words, the end surface 3400e covers or one side
edge of the end surface 3400e overlaps four vertices (corners) among the
five vertices (corners) of the NFL-generating end surface 36a except
vertex NFP. As a result, only the vertex NFP among the five vertices
(corners) is at a distance from the end surface 3400e, and therefore is
capable of functioning as a NF-light emission point.

[0080]Since the end surface 3400e of the main magnetic pole 3400 and the
NFL-generating end surface 36a are in contact with each other as
described above, the distance DWN in Z-axis direction between the
vertex WFP of the end surface 3400e that is the write-field generating
point and the vertex NFP of the NFL-generating end surface 36a that is
the NF-light emission point is equal to the thickness in Z-axis direction
of the NFL-generating end surface 36a in the bottom of the groove 51. The
bottom of the groove 51 of the surface plasmon generator 36 is at a
distance from the propagation edge 360 in the direction along the track
(in Z-axis direction). Since the thickness in the bottom of the groove 51
is equal to the difference (TNF-dGR) between the thickness
TNF of the surface plasmon generator 36 and the depth dGR of
the groove 51, it follows that

DWN=TNF-dGR (1)

Here, reduction in the amount of light to be converted to NF-light due to
partial absorption of waveguide light into the main magnetic pole 3400
made of a metal can be prevented by ensuring a certain distance DMW
(=TNF+TBF) between the portion of the main magnetic pole 3400
that is not embedded in the groove 51 and the waveguide 35. This applies
especially to a distance DMW in the case that the main magnetic pole
3400 is longer than the surface plasmon generator 36 in X-axis direction
as shown in FIG. 6 later. It can be seen from expression (1) that, in
order to ensure a sufficiently close distance between vertices WFP and
NFP under the condition that TNF is kept at a predetermined value to
provide a required distance DMW, the depth dGR of the groove 51
is chosen to be sufficiently large. As will be described later with
respect to practical examples, the distance DWN between the vertex
WFP that is the write-field generating point and the vertex NFP that is
the NF-light emission point is preferably 30 nm or more, and 100 nm or
less.

[0081]In summary, in the thermally-assisted magnetic recording head
according to the present invention, the distance between the vertex NFP
that acts as a heating point during writing and the vertex WFP that acts
as a writing point can be set to a sufficiently small value. This enables
a write field having a sufficiently large gradient to be applied to a
sufficiently heated portion in the magnetic recording layer of a magnetic
disk. Consequently, a thermally-assisted, stable write operation can be
ensured.

[0082]FIG. 6 shows a schematic view for explaining the thermally-assisted
magnetic recording utilizing a surface plasmon mode according to the
present invention. The figure shows a case that the main magnetic pole
3400 is alternatively longer in X-axis direction than the surface plasmon
generator 36. However, the principle of thermally-assisted magnetic
recording explained below apples to the respective embodiments shown in
FIG. 4 and FIG. 6.

[0083]Referring to FIG. 6, when the electromagnetic transducer 34 writes
data onto the magnetic recording layer of the magnetic disk 10, first,
laser light 53 emitted from the laser diode 40 of the light source unit
23 propagates through the waveguide 35. Next, the laser light (waveguide
light) 53, which has advanced to near the buffering portion 50, couples
with the optical configuration including the waveguide 35 with a
refractive index nWG, the buffering portion 50 with a refractive
index nBF and the surface plasmon generator 36 made of a conductive
material such as a metal, and induces a surface plasmon mode on the
propagation edge 360 of the surface plasmon generator 36. That is, the
waveguide light couples with the surface plasmon generator 36 in the
surface plasmon mode. Actually, evanescent light is excited within the
buffering portion 50 based on the optical boundary condition between the
waveguide 35 as a core and the buffering portion 50. Then, the evanescent
light couples with the fluctuation of electric charge excited on the
metal surface (propagation edge 360) of the surface plasmon generator 36,
and induces a surface plasmon mode, and thus surface plasmon is excited.
To be exact, there excited is surface plasmon polariton in this system
because surface plasmon as elementary excitation is coupled with an
electromagnetic wave. However, the surface plasmon polariton will be
hereinafter referred to as surface plasmon for short. The propagation
edge 360 is provided at the location closest to the waveguide 35 on the
inclined lower surfaces of the surface plasmon generator 36, and is a
corner edge where electric fields tend to concentrate; thereby surface
plasmon is highly likely to be excited. This surface plasmon mode can be
induced by setting the refractive index nBF of the buffering portion
50 to be smaller than the refractive index nWG of the waveguide 35
(NBF<NWG) and by appropriately choosing: the length (in
X-axis direction) of the buffering portion 50, that is, the length
LBF of the coupling portion between the waveguide 35 and the surface
plasmon generator 36; and the thickness TBF (in Z-axis direction) of
the buffering portion 50.

[0084]In the induced surface plasmon mode, surface plasmon 60 is excited
on the propagation edge 360 of the surface plasmon generator 36, and
propagates along on the edge 360 in the direction shown by arrow 61. Only
the propagation edge 360 among side edges of the surface plasmon
generator 36 is not covered or in contact with the main magnetic pole
3400, and therefore is not negatively affected by the pole 3400 that is
not adjusted so as to excite surface plasmon efficiently. As a result,
the surface plasmon can be propagated on the propagation edge 360 by
design.

[0085]As described above, by the above-described propagation of the
surface plasmon 60 in the direction of arrow 61 on the propagation edge
360, the surface plasmon 60, namely, electric field converges at the
vertex NFP of the NFL-generating end surface 36a, which reaches the head
part end surface 2210 and is the destination of the propagation edge 360.
As a result, NF-light 62 is emitted from the vertex NFP. The NF-light 62
is radiated toward the magnetic recording layer of the magnetic disk 10,
and reaches the surface of the magnetic disk 10 to heat a portion of the
magnetic recording layer of the magnetic disk 10. This heating reduces
the anisotropic magnetic field (coercive force) of the portion to a value
with which write operation can be performed. Immediately after the
heating, write field 63 generated from the main magnetic pole 3400 is
applied to the portion to perform write operation. Thus, the
thermally-assisted magnetic recording can be achieved.

[0086]In the magnetic recording, by intentionally propagating surface
plasmon on the propagation edge 360 and then generating NF-Light with
maximum intensity at the vertex NFP of the NFL-generating end surface
36a, the emitting position of NF-light 62 can be set to be sufficiently
closer to the position of generating write field 63. This enables a write
field having a sufficiently large gradient to be applied to a
sufficiently heated portion in the magnetic recording layer of the
magnetic disk 10. Consequently, a thermally-assisted, stable write
operation can be reliably performed.

[0087]Meanwhile, in a conventional case in which a NFL-generator provided
on the end surface of a head is directly irradiated with the laser light
propagating through a waveguide, most of the irradiating laser light has
been converted into thermal energy within the NFL-generator. In this
case, the size of the NFL-generator has been set smaller than the
wavelength of the laser light, and its volume is very small. Therefore,
the NFL-generator has been brought to a very high temperature, for
example, 500° C. (degrees Celsius) due to the thermal energy. As a
result, there has been a problem that the end of a read head element,
which reaches the opposed-to-medium surface, becomes relatively far apart
from the magnetic disk due to the thermal expansion of the generator,
which makes it difficult to properly read servo signals during recording
operations. Further, there has been another problem that the light use
efficiency is degraded because thermal fluctuation of free electrons
increases in the NFL-generator.

[0088]On the contrary, in the thermally-assisted magnetic recording
according to the present invention, a surface plasmon mode is used, and
NF-light 62 is generated by propagating surface plasmon 60 toward the
head part end surface 2210. This brings the temperature at the
NFL-generating end surface 36a to, for example, about 100° C.
during the emission of NF-light, the temperature being drastically
reduced compared to the conventional. Thus, this reduction of temperature
allows the protrusion of the NFL-generating end surface 36a toward the
magnetic disk 10 to be suppressed; thereby favorable thermally-assisted
magnetic recording can be achieved.

[0089]Furthermore, the length LBF of the whole buffering portion 50,
that is, the portion through which the waveguide 35 and the surface
plasmon generator 36 are coupled with each other in a surface plasmon
mode, is preferably larger than the wavelength λL of the laser
light 53. In this preferable case, the coupled portion has an area
markedly larger than a so-called "focal region" in the case that, for
example, laser light is converged on a buffering portion and a surface
plasmon generator and coupled in a surface plasmon mode. Therefore, the
configuration quite different from the system including such "focal
region" can be realized in the present invention; thus, very stable
coupling in the surface plasmon mode can be achieved. The induction of a
surface plasmon mode is disclosed in, for example, Michael Hochberg, Tom
Baehr-Jones, Chris Walker & Axel Scherer, "Integrated Plasmon and
dielectric waveguides", OPTICS EXPRESS Vol. 12, No. 22, pp 5481-5486
(2004), U.S. Pat. No. 7,330,404 B2, and U.S. Pat. No. 7,454,095 B2.

[0090]FIGS. 7a to 7d show schematic views illustrating various embodiments
regarding the NFL-generating optical system and the main magnetic pole
according to the present invention. Here, FIGS. 7a and 7b are
cross-sections taken by YZ-plane, and FIGS. 7c and 7d are cross-sections
taken by ZX-plane.

[0091]Referring to FIG. 7a, a portion 71a of a main magnetic pole 71 that
has a cross-section of substantially rectangular (square) shape is
embedded in a groove of a surface plasmon generator 70. Accordingly, the
main magnetic pole 71 is in surface contact with all side surfaces of the
surface plasmon generator 70 that do not have a propagation edge 700 as
one of their boundaries. In this embodiment, on the head part end surface
as an opposed-to-medium surface, the distance between the edge (where
write field is generated) of the bottom 710 of the main magnetic pole
portion 71a and the end point of the propagation edge 700 (where NF-light
is generated) can be set sufficiently small. This enables a write field
having a sufficiently large gradient to be applied to a sufficiently
heated portion in the magnetic recording layer of a magnetic disk. This
ensures a stable, thermally assisted write operation. A cross-section of
the main magnetic pole portion 71a can have any of various other shapes.
However, a cross-sectional shape that has a vertex at the bottom of the
groove 51 of the surface plasmon generator 36, as shown in FIGS. 4 and 5
in which the main magnetic pole portion 3400a has an inverted-triangular
shape, enables the write-field generating portion to be made very small
(vertex WFP in FIG. 5).

[0092]Referring to FIG. 7b, a surface plasmon generator 72 has a
cross-section of substantially triangular shape and does not have a
groove. A main magnetic pole 73 has a cross-section of substantially
rectangular (square) shape, and is located in contact with the surface
plasmon generator 72 and on the side opposite to the waveguide 35 in
relation to the generator 72. In the present embodiment, the main
magnetic pole 73 is in surface contact with a surface portion of the
surface plasmon generator 72 that does not include the propagation edge
720. In other words, the main magnetic pole 73 is in surface contact with
the side surface of the surface plasmon generator 72 that does no have
the propagation edge 720 as one of its boundaries, that is, the side
surface 721. In this case, on the head part end surface 2210, the
distance between the edge (where write field is generated) of the bottom
730 of the main magnetic pole 73 and the end point of the propagation
edge 720 (where NF-light is generated) is equal to the thickness T72
of the surface plasmon generator 72 in Z-axis direction. Accordingly, the
write-field generating portion and the NFL-generating portion can be
located sufficiently close to each other by choosing the thickness
T72 to be as small as possible.

[0093]Referring to FIG. 7c, a portion 75a of a main magnetic pole 75 is
embedded in a groove of a surface plasmon generator 74. The main magnetic
pole 75 is in surface contact with all side surfaces of the surface
plasmon generator 74 that do not have a propagation edge 740 as one of
their boundaries. Furthermore, the surface plasmon generator 74 is
tapered down toward the head part end surface 2210 in Z-axis direction in
such a manner that the propagation edge 740 inclines upward as it
approaches the head part end surface 2210. Referring now to FIG. 7d, a
portion 77a of a main magnetic pole 77 is embedded in a groove of a
surface plasmon generator 76. The main magnetic pole 77 is in surface
contact with all side surfaces of the surface plasmon generator 76 that
do not have a propagation edge 760 as one of their boundaries. Further,
the surface plasmon generator 76 is tapered in Z-axis direction toward
the head part end surface 2210 in such a manner that the surface on the
side opposite to the propagation edge 760 inclines downward as it
approaches the end surface 2210. Accordingly, the main magnetic pole 77
inclines downward towards the head part end surface 2210. In the
embodiments shown in FIGS. 7c and 7d, the distance DMW between the
portion of the main magnetic pole that is not embedded in the groove and
the waveguide 35 can be set larger while the write-field generating
portion and the NF-light generating portion are located sufficiently
close to each other by choosing the thickness of the surface plasmon
generator at the head part end surface 2210 to be sufficiently small.
This can circumvent the problem of reduction in the amount of light to be
converted to NF-light due to partial absorption of waveguide light into
the main magnetic pole. In the embodiment in FIG. 7d, the propagation
edge 760 linearly extends toward the head part end surface 2210 to avoid
the propagation loss that would otherwise be caused by a curvature of the
edge.

[0094]FIGS. 8a to 8f show schematic views illustrating an embodiment of
processes for forming the surface plasmon generator 36 having the groove
51 and the main magnetic pole 3400 according to the present invention.
The figures depict cross-sections taken by YZ-plane.

[0095]First, as shown in FIG. 8a, a groove 81 having a V-shaped
cross-section is formed in an already provided overcoat layer 80 made of,
for example, Al2O3 (alumina) covering a waveguide 35 made of,
for example, TaOx by performing an etching such as a reactive ion
etching (RIE) with CF4 as a reactive gas and with a given mask.
Then, as shown in FIG. 8b, an insulating film 82 made of, for example,
Al2O3 (alumina) is formed to cover the groove with use of, for
example, a sputtering. A portion of the insulating film 82 will later
define a gap, that is, a buffering portion 50, between the waveguide 35
and the surface plasmon generator 36.

[0096]Then, as shown also in FIG. 8b, an adhesion layer 83 made of Ta is
formed with a thickness of, for example, approximately 1 nm so as to
cover the formed insulating film 82. After that, a metal layer 84 made
of, for example, Ag or an alloy of Ag is formed on the adhesion layer 83
and at least in the groove 81 by using, for example, a sputtering. A
portion of the metal layer 84 will later constitute the surface plasmon
generator 36. Then, as shown in FIG. 8c, an electrode film 85 made of a
magnetic material such as FeCo, which will constitute a main magnetic
pole, is formed with a thickness of, for example, approximately 50 nm so
as to cover the metal layer 84. After that, a magnetic layer 86 made of a
magnetic material such as FeCo, which also will constitute the main
magnetic pole, is formed with a thickness of, for example, approximately
0.5 μm by using, for example, a plating. Then, as shown in FIG. 8d,
the entire surface is etched by a dry etching such as an ion milling to
expose the insulating layer 82 in the regions except the groove 81. As a
result, the surface plasmon generator 36 is formed, and the remaining
portion of the electrode film 85 and the magnetic layer 86 constitute a
portion 3400a of the main magnetic pole 3400 that is embedded in the
groove formed in the surface plasmon generator 36.

[0097]Then, as shown in FIG. 8e, an electrode film 87 made of a magnetic
material such as FeCo, which will constitute the main magnetic pole, is
formed again, and then a magnetic layer 88 is formed by using, for
example, a plating. Next, an overcoat layer 89 made of, for example,
Al2O3 (alumina) is formed by using, for example, a sputtering
so as to cover the formed magnetic layer 88. After that, a polishing
method such as a chemical mechanical polishing (CMP) is used to planarize
the surface to complete the main magnetic pole 3400.

[0098]It is understood that the forming method described above can be used
to provide a thermally-assisted magnetic recording head 21 having a main
magnetic pole 3400, a part 3400a of which is embedded in a groove 51
provided in a surface plasmon generator 36 to ensure that the NF-light
emission point can be located sufficiently close to the write-field
generating point.

Practical Example

NF-Light Intensity

[0099]Hereinafter, practical examples will be described in which
generation of NF-light in a NFL-generating optical system of the
thermally-assisted magnetic recording head according to the present
invention was analyzed in simulations.

[0100]The simulation analysis experiment was conducted by using
three-dimensional Finite-Difference Time-Domain (FDTD) method, which is
an electromagnetic field analysis. FIG. 9 shows a schematic view
illustrating a system used in the simulation analysis experiment.
Referring to in FIG. 9, laser light that entered a waveguide 90 was a
TM-polarized Gaussian beam having a wavelength λL of 823 nm,
the TM-polarization having the electric-field oscillation direction of
the laser light perpendicular to the layer surface of the waveguide 90,
that is, in z-axis direction. The intensity IIN of the laser light
was 1.0 (V/m)2.

[0101]The waveguide 90 had a width WWGZ of 0.5 μm and a thickness
TWG of 0.4 μm, and was made of TaOx, (with a refractive
index nWG of 2.15). A surface plasmon generator 91 had a thickness
TNF of 120 nm, and was made of Ag. The real part of the refractive
index of the Ag was 0.182 and the imaginary part was 5.370. The vertex
angle θNF at the vertex NFP on the head part end surface 2210
of the surface plasmon generator 91 was 75 degrees) (°). The
curvature radius of the propagation edge 910 was 15 nm. The clad portion
of the waveguide 90 including a buffering portion 93 was made of
Al2O3 (refractive index n=1.65). The buffering portion 93 had a
thickness TBF of 50 nm. The length LBF (in X-axis direction) of
the buffering portion 93 sandwiched between the waveguide 90 and the
surface plasmon generator 91 was 1.5 μm, which was the same as the
length of the main magnetic pole 92. The main magnetic pole 92 was made
of FeCo. The real part of the refractive index of the FeCo was 3.08 and
the imaginary part was 3.9. The width WMP in the track width
direction (in Y-axis direction) of the main magnetic pole 92 was 240 nm.

[0102]Under the experimental conditions described above, there was
measured, by the simulation, the relationship between: the distance
DWN between the vertex NFP that was the NF-light emission point of
the surface plasmon generator 91 and the vertex WFP that was the
write-field generating point of the main magnetic pole 92; and the
intensity of NF-light emitted from the vertex NFP.

[0103]Table 1 shows the result of simulation measurements of the
relationship between the distance DWN and the intensity ratio
INF/IWG of the peak intensity INP of generated NF-light to
the peak intensity IWG of waveguide light. FIG. 10 shows a graph
illustrating the simulation measurement results listed in Table 1. The
peak intensity INF of NF-light and the peak intensity IWG of
waveguide light are values at the vertex NFP on the head part end surface
2210 and at the waveguide-light intensity peak point WGP, respectively
(FIG. 9).

[0104]As can be seen from Table 1 and FIG. 10, the NF-light peak intensity
INF and intensity ratio INF/IWG increase with increasing
distance DWN. Thermally-assisted magnetic recording in practice
using NF-light requires a ratio of the intensity of desired NF-light to
the intensity of waveguide light incidental to the NF-light of 5:1 or
higher in order to form only a desired recording pit. Therefore, it can
be seen that the distance DWN is preferably greater than or equal to
30 nm to ensure that the intensity ratio INF/IWG exceeds 5:1.
When the distance DWN is 20 nm, the peak intensity INF of
NF-light is less than a half of the value that can be obtained with a
distance DWN of 50 nm. Therefore, it will be understood that the
effect of reduction in the thickness of the surface plasmon generator 91
is crucial.

[0105]Experiments have shown that in order to apply a write field having a
required gradient to a sufficiently heated region in the magnetic
recording layer of a magnetic disk, the distance DWN needs to be
less than or equal to 100 nm. Therefore, it will be understood that the
distance DWN between the vertex NFP that is the NF-light emission
point and the vertex WFP that is the write-field generating point, that
is, the distance between the bottom of the groove in the surface plasmon
generator 91 and the propagation edge 910 is preferably 30 nm or more and
preferably 100 nm or less.

Practical Example and Comparative Example

Write Field Intensity

[0106]A practical example will be given next in which the intensity of
write field from the thermally-assisted magnetic recording head according
to the present invention was analyzed in simulation. For the purpose of
comparison, a comparative example will also be given in which there has
been analyzed, by simulation, the intensity of write field generated from
a magnetic recording head having a main magnetic pole that was not
embedded in a surface plasmon generator but spaced apart from the
generator.

[0107]FIGS. 11a and 11b show cross-sectional views taken by ZX-plane,
schematically illustrating thermally-assisted magnetic recording heads
used in the practical example and the comparative example, respectively.
FIG. 11c shows a cross-sectional view taken by XY-plane included in an
upper yoke layer, schematically illustrating the thermally-assisted
magnetic recording head used in the practical and comparative examples.

[0108]As shown in FIG. 11a, in the thermally-assisted magnetic recording
head used in the practical example, the length LMP of the main
magnetic pole 92 was 2 μm, the distance between the main magnetic pole
92 and a back contact portion 94 was 6 μm, and the length LBC (in
X-axis direction) of the back contact portion 94 was 2.5 μm. A portion
of the main magnetic pole 92 was embedded in a groove in the surface
plasmon generator 91. The distance DME between the portion of the
main magnetic pole 92 that is not embedded and the propagation edge 910
(vertex NFP) was 120 nm. The distance DWN between the vertex NFP
that is the NF-light emission point and the vertex WFP that is the
write-field generating point was 50 nm. As shown in FIG. 11c, the length
LUY (in X-axis direction) of the upper yoke layer was 12 μm, and
the width WUY in the track width direction (Y-axis direction) was 17
μm. The back contact portion 94 consisted of two sections and a
waveguide 90 passed through between them with a gap DBW of 2 μm
on each side. A write coil layer 95 (FIGS. 11a and 11c) was formed as a
helical coil disposed in such a way as to sandwich the upper yoke layer
therebetween.

[0109]On the other hand, as shown in FIG. 11b, the thermally-assisted
magnetic recording head used in the comparative example had the same
configuration and dimensions as the head shown in FIGS. 11a and 11c
except that the main magnetic pole 98 of the head in the comparative
example was not embedded in the surface plasmon generator 97 but was
spaced apart from the generator 97. The distance DME between the
edge 980 of the main magnetic pole 98 that was the write-field generating
portion and NFP (propagation edge 970) was 120 nm, which was the same as
the distance DME in the practical example in FIG. 11a.

[0110]FIG. 12 shows a graph illustrating intensity distributions of
effective write fields in the practical example and the comparative
example. The horizontal axis of the graph in the figure represents
location LDT on the head part end surface 2210 along the track (in
Z-axis direction). That is, the effective write field intensities are the
values obtained on the head part end surface 2210. The origin of the
locations in the practical example is at the leading-side end of the
portion of the main magnetic pole 92 that is not embedded. The origin of
the locations in the comparative example is at the edge 980 of the main
magnetic pole 98. The positive direction is the down track direction (+Z
direction), that is, the direction heading toward the trailing side.
Further, the effective write field is defined as a write field generated
from the main magnetic pole that effectively acts on the recording layer
to reverse magnetization of the recording layer thereby to form a
recording pit. In practice, the effective write field HEFF depends
on three write field components HP, HT and HL as
HEFF=((HP2+HT2)1/3+HL2/3)3/2-
. Here, HP is a write field component in the direction perpendicular
to the surface of the magnetic recording layer, HL is a write field
component in the track width direction, and HT is a write filed
component in the direction along the track.

[0111]As shown in FIG. 12, the peak corresponding to the magnetic field
from the trailing edge of the main magnetic pole appears around location
LDT=0.25 μm in both of the practical and comparative examples.
This peak, which is not necessary for writing, is higher in the
comparative example than the practical example. On the other hand, the
effective write field intensity peak at the leading edge of the main
magnetic pole, which relates to writing, is over 15 kOe (Oersteds) in the
practical example, which is greater than the peak of approximately 14 kOe
in the comparative example.

[0112]Further, the effective write field intensity HEFF in location
LDT=-0.12 μm, which corresponds to the vertex NFP, that is, the
NF-light emission point, is 8.986 kOe in the practical example, which is
greater than twice the value in the comparative example of 4.119 kOe.
This shows that a sufficiently intense write field can be generated at
the NF-light emission point by embedding a portion of the main magnetic
pole 92 in the surface plasmon generator 91 and thereby a magnetic
recording head better suited for thermally-assisted magnetic recording
than ever can be provided.

[0113]As described above, it is understood that a thermally-assisted
magnetic recording head is provided, in which the NF-light emission point
can be provided sufficiently close to the write-field generating portion
thereby appropriately heating a portion to be written on the magnetic
recording medium. Thus, satisfactory thermal-assisted magnetic recording
can be achieved, which contributes to the achievement of higher recording
density, for example, exceeding 1 Tbits/in2.

[0114]All the foregoing embodiments are by way of example of the present
invention only and not intended to be limiting, and many widely different
alternations and modifications of the present invention may be
constructed without departing from the spirit and scope of the present
invention. Accordingly, the present invention is limited only as defined
in the following claims and equivalents thereto.